The present invention relates to a pipe inner-surface inspecting apparatus for use in inspection for damage or the like on the inner surface of an elongated small-diameter pipe such as, for example, a covering pipe for a nuclear fuel bar, or the like.
A covering pipe for a nuclear fuel bar is formed by an elongated small-diameter pipe having an inner diameter on the order of 9 mm. The inventors of this application have already proposed an apparatus for inspecting an inner surface of an elongated small-diameter pipe visually, in Japanese Utility Model Application No. SHO 61-80718. As shown in FIGS. 2 through 5 of the accompanying drawings of this invention, the apparatus comprises a bore scope 2 serving as a body inserted into the interior of the pipe 1 that is the subject of inspection, and a transparent glass means 3 that supports a reflecting mirror 4 which is arranged at a location spaced a predetermined distance from the forward end of the bore scope 2. The apparatus will be described below in brief.
As shown in FIGS. 2 and 3, the bore scope 2 has an image transmitting path 6 at the center of a stainless steel tube 5 whose outer diameter is slightly less than the inner diameter of the pipe 1. The image transmitting path 6 is formed by an optical fiber bundle or a combination of a plurality of lenses. The image transmitting path 6 has a forward end at which a concentrating lens system 7 is arranged. The concentrating lens system 7 has a visual field angle within the range .theta.. Arranged about the outer periphery of the image transmitting path 6 is a cylindrical light guide 8 which is composed of an optical fiber bundle. The light guide 8 has a rearward end which is optically connected to a light source (not shown). A forward end of the light guide 8 is formed into an illuminating section 8a for emitting light transmitted from the light source, axially into the pipe 1.
The transparent glass means 3 serving as transparent glass means is cylindrical in shape having a diameter substantially equal to the outer diameter of the bore scope 2. The transparent glass means 3 has one end end thereof which is mounted to the forward end of the bore scope 2 in contact therewith. The other end of the transparent glass means 3 is formed with a conical recess 3a. The conical recess 3a is formed to have a predetermined angle determined on the basis of the optical system and the illuminating system of the bore scope 2. The conical recess 3a is spaced a distance from the forward end of the bore scope 2. A portion of the conical surface of the recess 3a, except for a central or bottom portion and an edge portion thereof, is coated with a silver coating or the like to form or finish a reflecting mirror 4. The reflecting mirror 4 is so arranged as to diverge away from the forward end of the bore scope 2.
A guide member 9 made of resinous material or the like is fixedly mounted to the conical surface 3a of the transparent glass means 3 which is formed into the reflecting mirror 4. Specifically, the guide member 9 has an outer peripheral surface 9a which is in contact with the inner peripheral surface of the pipe 1, and a conical section 9b complementary to the conical surface 3a of the transparent glass means 3 which is formed into the reflecting mirror 4. The conical section 9b is in close contact with the conical surface 3a of the transparent glass means 3.
Further, as shown in FIG. 5, the pipe 1 is mounted on the upper surface of a fixing table 10. The fixing table 10 has one end thereof at which a base 12 is arranged. Arranged within the base 12 is an inserting device 11 for inserting the bore scope 2 and the transparent glass means 3 into the pipe 1. The inserting device 11 is composed of a plurality of support rollers 13 for supporting the bore scope 2 and the transparent glass means 3, and a drive mechanism 14 for inserting the bore scope 2 and the transparent glass means 3 into he pipe 1. Arranged at an end of the base 12 on the side to the other end of the fixing table 10 is an inserting and positioning section 15 for inserting the bore scope 2 into the pipe 1. The bore scope 2 has a rearward end to which an industrial television camera 16 is fixedly mounted. The television camera 16 has an image capture lens system which is connected to the rearward end of the image transmitting path 6 in the bore scope 2. The image on the television camera 16 is sent to an automatic inner-surface image processor 17 which comprises a video tape recorder 18 for recording the image, a monitor television 19 for displaying the image, and an operating panel 20 for operating these instruments 18 and 19. Predetermined processing of the image is carried out by the automatic inner-surface image processor 17.
The conventional pipe inner-surface inspecting apparatus is constructed as described above. With such a construction, when the driving mechanism 14 of the inserting device 11 is operated to insert the transparent glass means 3 and the bore scope 2 into the pipe 1 at the head of the guide member 9, the light emitted from the illuminating section 8a of the light guide 8 in the bore scope 2 passes through the transparent glass means 3 and is reflected by the reflecting mirror 4, thereby brightly illuminating the entire periphery of the inner surface of the pipe 1. An image of the entire periphery of the inner surface of the pipe 1 is reflected by the reflecting mirror 4 and reaches the concentrating lens system 7 at the forward end of the bore scope 2. The image reaching the concentrating lens system 7 is transmitted to the television camera 16 through the image transmitting path 6.
In the case of the conventional apparatus, as shown in FIG. 2, a range of the inner peripheral surface of the pipe 1, reaching the concentrating lens system 7, that is, a viewing range thereof is the section indicated by the character A which is composed of a portion A.sub.1 and a portion A.sub.2. The portion A.sub.1 is the portion reflected by the reflecting mirror 4 and is reflected in approximately a straight line. The portion A.sub.2 is the portion of the inner peripheral surface of the pipe 1 which is directly reflected by the inner peripheral surface of the pipe 1 into the concentrating lens system 7. In an image in which the range A is transmitted to the television camera 16, as shown in FIG, 4, the entire image A.sub.1 reflected by the reflecting mirror 4 is cast on the central region of the television camera 16, and the entire peripheral image A.sub.2 which is directly reflected into the concentrating lens system 7 is cast on the outside of the image A.sub.1.
Under these circumstances, when the driving mechanism 14 is operated to cause the transparent glass means 3 and the bore scope 2 to advance into the pipe 1, the entire peripheral image of the inner surface of the pipe 1 is continuously taken out through the entire length of the pipe 1 and is transmitted to the television camera 16. The image of the inner surface of the pipe 1, which is transmitted to the television camera 16, is displayed on the monitor television 19 in real time. A defective portion or portions of the inner surface of the pipe 1 are found by the image processing. The image processing is recorded by the video tape recorder 18. Thus, it is possible to judge or determine as to whether or not a damage or damages such as mars or cracks occur in the inner surface of the pipe 1.
In the conventional pipe inner-surface inspecting apparatus, however, it is difficult to accurately finish the central portion of the conical recess 3a of the transparent glass means 3 with which the reflecting mirror 4 is in close contact. Further, there is also a problem that halation occurs due to the light reflected at the central portion of the conical recess 3a. Moreover, since the pipe inner surface is generally mirror-finished, defective portions of the inner surface of the pipe 1 are more easily detected if the pipe inner surface is illuminated with a diffused light source.